A new study suggests up to 300,000 adults in the U.S. with type 2 diabetes may not know they have kidney problems because they do not show the classic signs of kidney disease commonly associated with diabetes.

Researchers say nearly half of all new kidney failure cases are attributed to type 2 diabetes. When diabetes isn't effectively managed through lifestyle modifications and drug therapy, the kidneys have a harder time doing their job in clearing wastes from the body, which often results in kidney disease and kidney failure.

Most doctors currently screen for kidney disease among adults with type 2 diabetes by testing for protein in the urine (albuminuria). And patients who have eye disease (retinopathy) are tested because they're also likely to have protein in the urine. Retinopathy is a condition associated with kidney disease caused by diabetes.

But researchers say much of what doctors know about the nature of kidney disease in people with diabetes is based on studies of people with type 1 diabetes rather than the more common type 2 diabetes. And their findings suggest that kidney disease among people with type 2 diabetes may have different features and characteristics than those found among people with type 1 diabetes.

The study, published in the June 25 issue of The Journal of the American Medical Association, looked at data from 1,197 people with type 2 diabetes over the age of 40.

Chronic kidney disease occurs when the kidneys are unable to eliminate toxins and waste from the body effectively and maintain a normal fluid balance. The severity of the condition is measured by estimating how well the kidneys are able to filter wastes in the blood, known as the glomerular filtration rate (GFR), and a low GFR is a clear sign of kidney disease.

Researchers found 13% of the adults with type 2 diabetes had a low GFR, but 30% of these patients did not have eye disease or protein in the urine. Therefore, the current screening procedures using these standard kidney disease indicators may be missing up to 30% of kidney disease cases among people with type 2 diabetes.